A The Hydrogeology of New York City

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The geology of the New York City counties is complex and varied. Geologic formations range from Precambrian bedrock the age of which can be measured in billions of years to glacial deposits that are less than twelve thousand years old to land filled areas that were created in the recent past. The stratigraphy of geologic units tends to be ordered with the younger formations resting on top of older formations. The oldest formations, the crystalline bedrock, such as granites and gneisses, form the "basement" rocks, with younger, softer rocks and unconsolidated deposits, such as sand, gravel and clay, resting on top of the basement. In New York City, the basement-rocks are generally inclined so that they are close to the land surface, or are the land surface, in the Bronx and Manhattan and parts of Queens and Richmond and slope downward towards the southeast. Southeastern portions of Queens and eastern portions of Kings counties are covered with sedimentary deposits with the bedrock as much as 1000 feet below the land surface in south Brooklyn and Queens.

If the "project site" is located in Manhattan or the Bronx, it is expected that the geo-exchange wells will be drilled into the bedrock since the likelihood of encountering usable quantities of granular aquifer materials in these counties is unlikely. Conversely, if the project site is located in southern Brooklyn or Queens, several productive unconsolidated aquifers exist in these locations. Therefore, either the project designer has the option of using extraction/diffusion wells or standing column wells.

Site C as shown on the map below is located adjacent to a mapped thrust fault, a fault in which one block (referring to the section of rock on one side of a fault and not to city blocks) is pushed over the top of another block. The symbol for a thrust fault used in the map above is a heavy line with a saw tooth pattern. The points of the saw tooth refer to the downward movement of the fault plane. Since these fault types generally produce shallow fault angles, a well drilled on the downward side of the fault line will encounter the fault plane further down as the location of the well is moved further away (in the direction of the saw tooth pattern, from the fault line. If the well is located on the upward side of the fault, the main (mapped) fault plane will be missed. However, since thrust fault systems tend to have multiple planes (like a stack of papers pushed from the side), it may be possible to develop a productive well on the "wrong" side of the fracture line. Again, just because the fault is mapped does not guarantee a productive well.

The section of the Baskerville Manhattan map, "Bedrock and Engineering Geology Maps of New York County and Parts of Kings and Queens Counties, New York, and Parts of Bergen and Hudson Counties, New Jersey", shown below is for an area north of Central Park. The box on the map indicates an area that is currently being investigated for geothermal potential. An 8 story apartment building with 130 dwelling units is planned for the site. The map indicates that the project site lies over a former swamp or marsh associated with a drainage channel or stream. During drilling of test wells, a productive gravel zone was discovered at the western end of the project site. The gravel was found to be absent less than 75 feet to the east. The presence and absence of the unconsolidated aquifer corresponds very well with the mapping. The mapping also shows a fault zone that crosses Manhattan starting at the Hudson River at 125th street and trends towards the southeast. The mapping indicates that the fault zone does not cross the project site, but turns south, away from the mapped drainage area, avoiding the project site. Several deep wells were drilled as test wells, for this project. The wells ranged from 600 feet to 900 feet deep and had yields ranging from 150 to 30 gallons per minute. It is clear from these results that these wells are tapping significant fractures, even though none are mapped in the immediate area of the project site. This illustrates the need for a thorough and careful analysis of any given site.

Working in bedrock areas, the Bronx and Manhattan and portions of Staten Island, requires design flexibility since the actual outcome of the drilling program cannot be predicted in advance. The system designer should assume that the wells to be drilled will not produce sufficient water for the project requirements and, therefore, the wells should be designed as standing column wells with minimal extraction. If, as described above, high yielding wells are developed, the depth of the wells can be limited in proportion to the yield of the wells.


The geology of Brooklyn and Queens is very different from the geology of the other boroughs. Where The Bronx, Manhattan and parts of Richmond are predominantly underlain by bedrock with little if any soil covering the rock surface, most of Queens and Brooklyn have very thick surficial deposits of unconsolidated material overlying the bedrock basement. These deposits range from clay to gravel and are from zero to over 1,000 feet deep. The sand and gravel aquifers include the Upper Glacial, Jameco, Magothy and the Lloyd. These aquifers areall extensively used as sources of ground water for eastern Long Island. The most widely used aquifer for municipal water supplies is the Magothy Aquifer. The Lloyd aquifer is the deepest aquifer, directly in contact with the underlying bedrock. The Lloyd is a restricted use, protected, aquifer only available for use by communities that have no other option for a water supply, such as barrier island communities that find their shallow wells become brackish. The New York State Department of Environmental Conservation will not allow the use of the Lloyd for extraction/diffusiontypr gsothermalwells. The Jameco and Upper Glacial aquifers are shalloweo lower peoduetivityaquifers that may be available for use depending on the project loration.

Table 1. Mtjoc hydrogeolog/c units of the Long Island groundwater cesecvo/c.

Hytrrgerlrgic Unit

Approximate Mrxiaua Thickness

Wrltr-Btrring Character

Upptr glacial aquifer Grrtiners Clry

400' 150'

Mainly sant ant gravel rf moderate tr high permeability; alsr includes clayey deposits rf lrw permeability. Clay, silty clay, ant a little fine sant rf lrw tr very lrw permeability.

Jrascr rquifer


Mainly aetiua tr crarse srnS rf arSsrrts tr high permeability.

Mrgrthy rquifer


Crarse tr fine srnS rf arterae permeability; lrcally crnlrini highly permeable gravel, ant ^unta!! silt ant clay rf lrw tr very lrw permeability.

Srrilrn Clry


Clay rf very lrw permeability; srae silt ant fine srnS rf lrw permeability.

Llryt rquifer


eant ant gravel rf arterae permeability; srae clayey material rf lrw permeability

Table from "pbisotopes.ess.sunysb.edu/geo101_f00/articles/ exam 2/ligr/ table1.htm - 4k

Table from "pbisotopes.ess.sunysb.edu/geo101_f00/articles/ exam 2/ligr/ table1.htm - 4k

All Long Island aquifers receive their fresh water from precipitation. Long Island receives, on average, about 44 inches of precipitation a year. Of this, about half of the precipitation, or approximately 22 inches of rain, percolates into the ground and is recharged into the groundwater system. The remaining precipitation is either evaporated, taken up by plants, or runs off into creeks, bays and estuaries. In areas where the water table and the ground surface meet, streams, ponds and wetlands are formed. In an undisturbed natural setting, (e.g., before human activities) all of Long Island's groundwater would ultimately reach the coast where the ground water would mix with and the ocean. This process is called underflow - due to human activity, this process has been significantly changed so that not all water in the ground water system is returned to the ocean.

Today, ground water is withdrawn from the system constantly. Over 138 billion gallons of water is taken each year from beneath Nassau and Suffolk Counties. In coastal areas, as water is drawn up for use, less groundwater is available to be discharged into the estuaries. The resulting loss of water and pressure allows saltwater from the ocean to flow into the aquifer, causing the ground water to become saline, resulting in a condition called "saltwater intrusion". New water from precipitation is constantly recharging, or replenishing, the aquifers. Unfortunately, as water recharges the system, it can easily carry contaminants with it into the ground water. Since it is the shallowest and closest to most sources of contamination, the Upper Glacial aquifer is the most heavily contaminated of the three. The next most seriously contaminated aquifer is the Magothy, which is the layer below the Upper Glacial. The Magothy aquifer supplies over 90% of the water used in Nassau County and about 50% of all water used in Suffolk County.

The heat exchangers which transfer heat in or out of the heat pump refrigerant should be of an alloy such as copper-nickel that experiences no ill effects from salinity or variation in pH. The contaminants in the ground water will have an effect on the maintenance requirements for the well and well pump. See Chapter 3, Description of Geothermal Heat Exchangers for a discussion of potential problems with open wells due to water quality and other factors.

Principal Hydrologie Units

The three principal aquifers of Long Island are (top to bottom) the Upper Glacial Aquifer, the Jameco, the Magothy Aquifer, and the Lloyd Aquifer.

Continental glaciers of Wisconsinan age (20 to 86 thousand years ago) brought to Long Island the materials that now comprise nearly all of its surficial sediments. Glacial material was deposited in two terminal moraines: the Ronkonkoma moraine, which forms Suffolk's "spine" and South Fork, and the Harbor Hill moraine, which runs along the North Shore and forms the North Fork. Some of the original glacial material (till) can still be seen along the north shore of the South Fork, at Montauk, and on Shelter Island, where it acts to retard the downward movement of recharge.

Most of the glacial material was reworked by meltwater to form large, sandy outwash plain deposits south of, and between, the two moraines. These highly permeable, stratified sand and unconsolidated deposits filled in the valleys eroded on the surface of the Magothy (although some filling may have occurred prior to the ice sheet's advance to Long Island).

The glacial deposits can reach thicknesses of up to 700 feet (e.g., in the "Ronkonkoma Basin"). They generally overlie Magothy deposits, except in areas of the North Shore where the Magothy was scoured away by glaciers, and in areas of the South Shore where the Gardiners Clay or Monmouth Group intervene.


Bedrock below Queens and Kings Counties is comprised of crystalline metamorphic rocks (gneisses and schists) that are similar to those found in Connecticut. The original basement rocks are believed to have been early Paleozoic (Cambro-Ordovician) to Precambrian granite or sandstone more than 400 million years old. These rocks were crystallized by heat and pressure during folding and faulting caused by tectonic forces during early Paleozoic time (200-300 million years ago).

The bedrock surface below Suffolk County is tilted southeast to south at a slope of approximately 50 to 70 feet per mile. It is, therefore, closest to land surface (subcropping) in northwest Queens and Brooklyn, and deepest along the South Shore (over 700 feet deep at the western part of Fire Island). In many places, the upper surface of the bedrock is weathered to a residual clay. Since the water bearing capacity of the unit is extremely low, the bedrock surface is considered to be the bottom of the groundwater reservoir.


The sediments comprising the Raritan Formation lie on the bedrock surface and are believed to have been derived from stream erosion of areas to the north and west during late Cretaceous time (60-100 million years ago). The formation is made up of a lower sand and gravel member (Lloyd Sand) and upper clay member (Raritan clay).

The Lloyd Sand Member has a moderate overall hydraulic conductivity and consists of sand and gravel interbeds, with occasional lenses of clay and silt. The Lloyd's beds are about parallel to the bedrock surface below. Its upper surface lies about 200 feet below sea level in northwest Queens, and over 900 feet below sea level at Rockaway. The unit is believed to terminate somewhere close to the North Shore beneath Long Island Sound, and is not found in Connecticut. The thickness of the Lloyd increases from north to south; it is about 100 feet thick in central Queens, and over 350 feet thick at Rockaway.

Clay Member of the Raritan Formation

The clay member of the Raritan Formation (Raritan clay) overlies the Lloyd Sand Member throughout Suffolk County. In some locations, however, the clay has been eroded, and glacial deposits overlie the Lloyd, thus providing good hydraulic conductivity between the glacial deposits and the Lloyd aquifer. The Raritan clay, although composed mainly of clay and silt, does contain some sand and gravel beds and lenses; overall, however, the hydraulic conductivity of the clay member is low, and it confines the water in the Lloyd aquifer.

The Raritan clay parallels the Lloyd Sand Member and terminates just offshore in Long Island Sound. The surface of the clay member lies between 0 and 100 feet below sea level in northwest Queens, and about 700 feet below sea level at Rockaway. Clay member thicknesses range between 50 and 100 feet in the northern areas, and reach nearly 300 feet in the western part of Fire Island.

Magothy Formation


The Magothy Formation - Matawan Group undifferentiated (informally "Magothy") is composed of river delta sediments that were deposited on top of the Raritan Formation during the late Cretaceous after a period of erosion. It consists of highly permeable quartzose sand and gravel deposits with interbeds and lenses of clay and silt that may have local hydrologic significance.

The Magothy was eroded during the time period between the end of Cretaceous and the Pleistocene. The surface was scoured by glaciers meltwaters that also shaped the Magothy's surface, creating north-south valleys. Unlike the upper surfaces of bedrock and the members of the Raritan Formation, the highly eroded upper surface of the Magothy does not exhibit any distinctive tilt to the southeast, although bedding planes within the formation have this orientation. Because the upper surface is so irregular, the thickness of the Magothy varies; however, the thickness generally increases from north to south, with the greatest thickness (around 1,000 feet) found along the South Shore.

Gardiners Clay

Gardiners Clay

The Gardiners Clay is a shallow marine or brackish-water deposit of late Pleistocene age. It is typically grayish-green to gray; the variation in color is due to the content of minerals such as glauconite. The unit contains some beds and lenses of sand and silt, but its overall hydraulic conductivity is low, making it a confining layer for underlying aquifer formations, particularly the Magothy.

The Gardiners Clay is found along most of the south shore. Its northern extent varies from 3 to 5 miles inland and is indented by long, narrow north-south channels, which indicate the effects of erosion by glacial meltwater streams and areas of nondeposi-tion. The upper surface of the unit ranges in altitude from 40 to 120 feet below sea level. The thickness of the unit increases southward toward the barrier island, reaching thicknesses of over 100 feet.

Long Island Hydrogeology


The Pleistocene Jameco Gravel unconformably overlies the Monmouth Group and is only present in western Long Island; its eastward extent just barely enters Nassau County. The Jameco Gravel attains thicknesses of 200 feet and is comprised of brown, fine to coarse grained sand and gravel. The Jameco Gravel may represent fluvioglacial deposits of Illinoian age associated with deposition in an ancestral Hudson River valley (Soren, 1978). The Jameco Gravel makes up the Jameco aquifer which is confined below the Gardiners Clay and displays a average horizontal hydraulic conductivity between 200 to 300 feet per day (Smolensky et al., 1989).

Long Island Hydrogeology


Exceptforasmallportion pfsarentaxdi mrofe depositad on Longlsland, the upper sectionci cedimenlson tl^eis^i^i^d r^na^^oflP^e^i^l^ec^tins^l^icMc^cii^c^s^^fiv^^i^^lXsvrre a resultef Wisconein ift^^ mlsclation.nhe upper glacial deposits lie unconformably atop the subcropping Matawan/Magothy, Jameco Gravel and Gardiners Clay.

Giaxidlsroui hascut dofniyintosubcroppinptosmations,perticnlarIymte the Matawan/Magothy section. The upper glacial deposits outcrop at the surface and rxpresexta dullrangpof aiacIaCdeppcitis>nal endisonmrcOffrommoixineto ouCwash jrioin toicoustsmo.Uppenglanial canrecca m^le]^(c]tne^^ The oaomorphology of Long Island is marked by the resultant hills of the Ronkonkoma and Harbor Hill moraines and gently sloping plains associated with glacial outwash depesiio Tneuoectnlatial desotitsmake up the Upper Glacial aquifer, which is the predominant source of private water supply wells. The moraines consist of till con^osod ofsand, clay and gravel and display an average horizontal hydraulic conauctiviryof 13n feetper dry(Smolensky et al., 1989). The highly permeable stratified drift of the outwash plains that lie south of the moraines consists of fine to very coarse grained quartzose sand and pebble to boulder sized gravel. The average horizontal hydraulic conductivity of the glacial outwash deposits is 270 feet per day (Smolensky et al., 1989).

Holocene deposits, which are as much as 50 feet thick and consist of salt-marsh deposits, stream alluvium, and beach sands, occur locally throughout the island. Holocene deposits consist of sand, clay, silt, organic muck, and shells. They are at land surface and generally overlie Pleistocene deposits. They are either unsaturated or too thin and discontinuous to form aquifers. In some areas, they form local confining units.

Geologic Unit



Upper Glacial Aquifer



Gardiners Clay (Kings & Queens Cnty)

confining unit

Jameco (Kings & Queens Cnty)


Monmouth Group (south shore)

confining unit

Upper Cretaceous

Magothy Formation


Raritan Fm - Clay Member

confining unit

The Bronx and Manhattan

The Bronx has been the subject of limited geologic explorations and, as a result, few geologic reports (Bulletin GW-32, 1953, Geology in the Bronx and Richmond Counties ... by N.M. Perlmutter and T. Arnow) exist that cover the geology of that borough. Similarly with Manhattan, the existence of a "city" in these boroughs has limited the amount of classic geologic studies that can be made. Charles Baskerville has produced a set of engineering geology maps that cover both the Bronx and Manhattan. Mr. Baskerville has used engineering data including data developed from the numerous tunneling projects, such as water tunnels, subway tunnels and power lines. Data from foundation borings for numerous projects such as building and bridge construction were also used. The mapping is intended to assist engineers in foundation design and is not intended to be a definitive geologic investigation. Mr. Baskerville does not devote much space to the identification and in depth description of geologic units (lithology). Instead, he does provide generalized descriptors for the various rock types that exist in the Bronx and Manhattan. More importantly, however, Mr. Baskerville has mapped the existence of bedrock features that bear more relevance to geothermal system. The locations of bedrock faults, bedding contacts and strata folds have been mapped. These features can improve the chances of developing higher than average yielding wells, which will, in turn, reduce the amount of drilling necessary to develop the necessary thermal exchange for the project. Please note that for "closed loop" systems the existence of highly productive fracture zones is irrelevant.


---Old PitMl fi:-il Aquectucïi— rorniur li shown incomfllace núnh û(

Mflíor Dtcgí n fcypresswoy because It .runenlly Is not In ust

SuWuv ' (or) rtihmui tunnel CtinsylitNiH'íl I i'iui Ciiinfh1rl> '..A- 1 unnel -----Sewer tunnel


---Old PitMl fi:-il Aquectucïi— rorniur li shown incomfllace núnh û(

Mflíor Dtcgí n fcypresswoy because It .runenlly Is not In ust

SuWuv ' (or) rtihmui tunnel CtinsylitNiH'íl I i'iui Ciiinfh1rl> '..A- 1 unnel -----Sewer tunnel


Fijrrnn drainage and shoreline—In bkie. Shown only whirrr different fawn present drainage and shoreline. Areas formerly under water are shown by dot pattern. Where extremity smalt, former ponds Are lahelSod "p " Straight line segments probably are furrows and ditch« buift to tower ihe water table

Forme* suramp or marsh — tn blue. Dashed line dufliw-, whem vj.vi3ii[> or ma»h adjoins higher ground, Extremely small occurrence are labelled


_ Contact between geologic unit*—Dashed where approximately loomed:

dotted where under water; queried where uncertain Whet« shown sofid under water, was located by test borings and tunnel data

- v r ■ Fault — Paired arrows show relative movement; U, upthrown side; D, 0 down thrown ad«. Dashed wher« approximately located; doited where underwater. (putridd u/hftre unc#ruin WhaM Man in tunnel, arrow shows inclined dip, and short line normal to fault trace shows vertical dip

—*-A— Thrust fault—Sawteeth on upper plate Djwhed whoro AppTOximAtslv located; dotted where under water Where- seen tn tunnel b shown wild Alternating eoW and open yiw&mth indiohW thrust fault« coincident in map view fnear Roosevelt (Welfare] Island: see sheti 11 —>*—Overturned thrust fauh —Sawteeth are on loweT plate, but point In direction oi movemervtof overturned tipper plate, bars are on upper plate <see sheet ], cross section A-A') Crush or shear «One encountered In uinltrt'ji uurid workings — Shows dip where known

Contours on the bedrock lurface—B«»*d on »me datum os topographic contours. Closed, hathured areas indicate depressions. Contour interval

10 A

f Single outcrop or area of closely spaced outcrops

The above map is a section of the Baskerville Bronx map centered on the Mosholu Park in north central Bronx. The map symbols are explained to the right of the map. As can be seen, this map contains a wealth of information usable to the designer of geothermal systems. The blue letters (A,B and C) indicate hypothetical locations considered for a geothermal system. Location "A" is in an area that indicates significant fracturing, shown by the black line that runs from the upper left corner of the map to the lower center of the map. The line is labeled with U/D at several locations. The U infers that that side of the fault is displaced upwards with respect to the other side of the fault, labeled D. In addition to the main line discussed above is a shorter east west fracture that is partially obscured by the letter A. Wells at the intersection of two, or more, fracture systems typically produce more ground water than wells that are located in areas free of fractures or adjacent to single fractures.

Site A is located over the mapped path of one of the City's water tunnels. Before attempting to drill a well in any location in New York, it is imperative that the possible existence of any underground utilities be discovered. Utilities can include currently active water tunnels, sewers, telephone and power lines, subway lines and steam pipes. In addition to active utilities, "old "unused or abandoned utilities may be found that may include any of the above listed. Therefore, before the drilling starts, the One Call Center for New York and Long Island should be called. Their number is 1-800-272-4480. For additional information and to setup safety seminars call 1-718-631-6700. They also have a WEB page with the address: WWW.OCUC.net. The One Call Center will mark the project site with the location of "member" utilities. A list of their members is provided on the WEB page. The New York City agencies, such as sewer and water, are not members and need to be contacted separately. Site B on the above map is not directly on any mapped faults or fracture systems. The results of drilling at this location should produce a well with an average yield of 20 gallons per minute, or less. However, the key term above is "mapped" fracture system. Just because a fracture system is not mapped it does not mean that a fracture system does not exist at that location. Generally a fracture is mapped when there is evidence of its existence, such as a linear valley, bedrock outcrops, or data developed from subsurface work. When such evidence is not available, the geologist may not know of the existence of a fracture system and, therefore, cannot map it. Therefore, the preliminary design should be for a standing column well, assuming that a low yield well will be drilled, but sufficient flexibility should be built into the design to allow for an alternate design if a high yield well system is drilled. Similarly, in location A, the existence of mapped fractures does not guarantee the production of high yield wells and the system design should be sufficiently flexible to allow for alternate configurations.

Richmond County

The geology of Staten Island is varied and complex, ranging from artificial fill, various glacial deposits including glacial till and glacial outwash, as well as exposed bedrock including ancient serpentines. The geothermal designer, with respect to particular locations in Richmond County, has the option of completing wells in the outwash deposits in eastern Staten Island or the completion of bedrock wells throughout most of the remainder of the borough. Portions of Staten Island are artificially filled wetlands and coastal areas that may contain transmissive deposits. However, it is more likely that the fill materials used are not sufficiently transmissive for water production.

The outwash deposits located in eastern Staten Island are similar to the outwash deposits found in southern Brooklyn and Queens. Both units are capable of ground water yields in the hundreds of gallons per minute to thousands of gallons per minute. However, unlike the Long Island outwash deposits, the outwash on Staten Island are limited to a maximum of 125 feet. The proximity of the outwash deposits to New York Bay places this aquifer in danger of salt water intrusion from over pumping. Therefore, a system of five New York City drinking water wells was limited to pumping less than 5 million gallons of water per day, although the wells were capable of significantly higher yields. These wells have not been operated since the early 1970's. Geothermal systems return the water pumped out to the aquifer, so they should not increase the risk of saltwater intrusion. Salty or contaminated water will increase the maintenance required for wells and well pumps.

The terminal and ground Moraines of Staten Island are generally composed of glacial till, a material that results from the grinding of rocks by the advancing glacial ice. The material, till, appears to be a hard clay with various amounts of sand and gravel mixed in. Till has poor hydraulic conductivity and should not be considered as a source of ground water. Occasionally sandy till is encountered. These deposits, although more productive than the clay tills discussed above, are still limited to about ten gallons per minute, on average (Soren 87-4048, 1988).

The Raritan Formation underlies the outwash deposits of eastern Richmond. Wells tapping this formation, which includes the Lloyd, or Farrington as it is referred to in New Jersey, have yields as high as 200 gallons per minute. This formation appears to be confined, separated from the water table aquifer, but insufficient data exists to fully make that determination.

The bedrock units underlying Richmond include the Newark Supergroup (shales, sandstones and limestones), the Palisades Diabase, the Manhattan Schist and the Staten Island Serpentine. Ground water data from the Staten Island portion of the Newark Supergroup is not generally available and, therefore, the yield of this formation within Richmond is not known. However the Newark formations is tapped extensively in Rockland County New York and is found to have an average yield of 83 gallons per minute (Permutter, 101-120, 1959). This average yield is based on a list of wells, which include mostly municple wells, including a well yielding a reported

1,515 gallons per minute. If all wells, including domestic wells, tapping this formation were included in the average, the average yield for the formation will be found to be considerably lower, more in the range of 10's of gallons per minute.

The Palisades Diabase is considered a poor water producing formation with yields limited to less than 10 gallons per minute. The Manhattan Schist unit in Richmond is not generally used for water supply due to the existence of more productive unconsolidated deposits. However, wells drilled in the Manhattan Schist in Manhattan and Westchester generally produce yields of between 5 and 50 gallons per minutes, with some wells yielding as high as 150 gallons per minutes. The productivity of this unit is completely dependant on the existence of faults and fractures that may be tapped by the well.

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QMitduE-jLai-V I'll aO 1 iiL

¡5 t PV = W 4 i* = llnd-1 t H lb D'lai'lnJilLltTlL

HnwfllLX O t' u II ^ ( Unfllvi d-TtJ> i_l r n n v i l± 1 rtll 5 '' L L ' ' I 1 1> ) to ccmbcicir H. Y. t ■ i: I- OUp C UrtdlVldiiJJ

Brooklyn Queens Aquifer


The hydrogeology of the City of New York is complex and varied presenting an interesting challenge for the design and implementation of geothermal systems. Since the location of the intended system is critical in determining the nature of the geology and, consequently, the type of well that will be used for the system, the designer must consult the mapping that is in this chapter or additional mapping listed at the end of the chapter. It is important that a hydrogeologist is consulted at the initiation of the design process so that the nature and extent of the drilling can be assessed early.

The cost of well drilling is affected by many variables including non-geotechnical factors such as site access and noise restrictions. Various geologic environments present difficulties to the driller that will extend the amount of time necessary to complete a well. A well drilled in an area that has bedrock close to the land surface is considerably easier to drill than a well that has to first penetrate many feet of unconsolidated deposits. The boring through the unconsolidated deposits must be kept open so that the formation does not fall into the boring, locking the drill tools into the earth. This is done by either using high density drilling fluids to drill through the earth or by installing steel casing as the boring is drilled. If the objective is to tap an unconsolidated aquifer, the well must be finished with a well screen to hold back the aquifer material while letting in the ground water. Bedrock wells, in most cases, do not require well screens. However, bedrock wells generally do not produce as much water as wells screening unconsolidated deposits. Therefore, bedrock wells will be significantly deeper than gravel wells.

Certain sections of New York are underlain by highly productive unconsolidated aquifer materials. Wells tapping these aquifers can produces prodigious quantities of water, limiting the amount of drilling necessary for the project. However, if the underlying aquifer is the Lloyd, as it is in parts of north/central Queens, the New York State Department of Environmental Conservation will not issue a permit for use of the Lloyd, since it is a highly protected aquifer. In that case, it is necessary to utilize any overlying aquifer material, if available, or to drill through the Lloyd, isolating the aquifer with steel casing, and continue into the underlying bedrock.

The following reports were referenced in this chapter:

Buxton, H.T., Shernoff, P.K., 1999,Ground-Water Resources of Kings and Queens Counties, Long Island, New York, U.S. Geological Survey Water Supply Paper 24978, 113p, 7 plates

Buxton, H.T., Soren, J., Posner, A., Shernoff, P.K., 1981, Reconnaissance of the Ground-Water Resources of Kings Queens Counties, New York, U.S. Geological Survey Open Report 81-1186, 59 p.

Bedrock and Engineering Geologic Maps of Bronx County and Parts of New York and Queens Counties, New York, Charles Baskerville, Miscellaneous Investigation Series, Published by the U.S. Geological Survey, 1992.

5. b Choosing a geoexchanger


Brooklyn and Queens, and any site with a similar geology, are well suited to the geothermal earth coupling formed by a supply and a diffusion well. A requirement of 3 gpm per dominant ton is required from the supply well and a responsible diffusion well must be capable of receiving this flow rate. It should be noted the typical diffusion well is "double the size" of the supply well. This increase in size is attributed to the relative hydrologic potential between a well with a depressed source cone around the well head as compared to the impressed diffusion cone around the return well.

The diameter of the impressive and depressive cones are a function of the permeability of the surrounding geological strata. The only limiting factors to these type systems is the availability of 3 gallons per minute per connected heat pump ton of flow and a responsible method of returning the water to the environment. Aquifer testing and modeling may be necessary if large, multiple well systems are to be installed. This will allow a proper design which avoids overlapping cones and provides sufficient water flow. Typical design temperatures for the New York City area are 50°F well water the year around, heating and cooling season (ARI standards rate at 50°F all year around; new ISO standards rate cooling at 59°F and heating at 50°F entering water).

Attention must be paid to the source of the water being returned to any given aquifer. Earth recharge via septic or sewers is not permitted. The Upper Glacial Aquifer which lies closest to the surface in Brooklyn and Queens may carry both natural and industrial contaminants. The Lloyd aquifer which is the next aquifer down is considered to be pure and uncontaminated cannot be used as a diffusion well if the source water is not also the Lloyd Aquifer. See also the section on permitting. Existing installations east of the East River favor this two-well system. See the description below of the four Long Island Power Authority buildings.


Sites where a concern for surface or ground water quality exists typically utilize closed loop systems. These vertical or horizontal closed loop earth coupling systems are designed to move an antifreeze solution through a series of loops arranged either vertically or horizontally. The material used for this piping is high density plastic pipe with a low friction loss and consequent low pumping effort1. This method is employed in areas with polluted water, e.g. do not meet primary drinking quality standards are encountered. Closed loop systems are somewhat less efficient and more costly. There is a trade off between loop pipe length and minimum design temperature. Existing ARI (ARI-330) and ISO (ISO-13256) standards specify design temperatures at 32°F for the heating season and 77°F for the cooling season.

Horizontal closed loops take one of two forms either a straight pipe of approximately 1,000 linear feet per ton, out and returned to the heat pump in a 4-6 foot deep 500 foot trench or a more recent and popular method call the Slinky®. The Slinky® also employs approximately 1,000 linear feet of high density polyethylene pipe but it is coiled and the extended as a flat map similar to child's slinky toy. In this manner an 80-100 foot trench can be loaded with 1,000 feet of pipe providing a one ton capacity. Generally, if trenching is easily achieved and no sharp rocks exist, a horizontal earth coupling system can be less costly than other systems, with the exception of the two well system described above. Typical Slinky®. Installation is shown in figure 2b-4

Vertical Closed Loop earth coupling utilizes the same design specifications and piping methods and material. Antifreeze solutions in the loops are also required. As the earth is warmer at depth, the heating dominated vertical closed loops typically require only 300-400 linear feet of pipe per ton, see figure 5. The average practical heating dominated borehole is 300-400 feet deep, this implies approximately two tons capacity per bore hole.

A cooling dominated vertical closed loop may require nearly twice that length. (keeping in mind a cooling load not only must remove the sensible and latent loads of the building, but also must remove the inductive heat generated by the heat pump's motors.)

See appendix C for the software modeling available for closed loop systems. Loop length and commensurate cost are reduced as the design temperature limits are further away from the average earth temperature, 51°F in this example.

Performance and efficiency of a typical heat pump in the heating mode at 30°F versus operation at 20°F can be reduced by 15%2. In the cooling mode at 70°F vs. 90°F the reduction in performance is approximately 9%, with a reduction in efficiency of approximately 25%! In this example, these penalties are offset by a reduction on total closed loop length by approximately 80 feet per ton for heating and 90 feet per ton for cooling requirements.

While reducing the cost of the loop field is an important design factor, it also can severely impinge upon a design safety margin. Designing at the heat pump's minimum or maximum entering temperature limits provide no design. An unusually cold winter or hot/moist summer can place a higher demand on the closed loop than published design conditions, leaving no capacity in the ground loop and driving the loop temperatures beyond the heat pump's design capabilities.

Closed loop systems, are designed for heat pump evaporators operating at or below 32°F, e.g. entering water temperatures below approximately 38°-39°F. Because of the probability of creating ice in a heat pump's evaporator heat exchanger, good closed loop design practices require an antifreeze be added to the closed loop. While the antifreeze will somewhat decrease efficiency it permits the heat pump to operate at these lower temperatures. Antifreeze solutions are typically designed for temperatures 10°F lower than the minimum entering water solution. A common solution of 20% ^^ food grade propylene glycol, this solutions provides an 18°F freezing point. This implies a minimum of 28°F (i.e. +10°F) minimum entering water temperature from the ground loop.

We recommend the use of propylene glycol as it is not a pathenogenic poison and is environmentally friendly. However, propylene glycol solution tends to become increasingly viscous as temperatures go below 35°F. The designer must consider this increase in viscosity when designing ground loop pumping.

Other antifreezes without the increased viscosity effect, as methyl alcohol (methanol) are equally effective as antifreeze agents, however, its designation as a poison and flammability do not recommend this compound. Several ethyl alcohol (ethanol) based compounds are also available to the designer. Use of these antifreeze solutions should be tempered with a review of the denaturants used in the ethanol solution. Some of ethanol's denaturants are equally poisonous as methanol.


Standing column wells consist of a borehole that is cased until competent bedrock is reached. The remaining depth of the well is then self-supporting through bedrock for the remainder of its depth. A central pipe smaller than the well diameter is dropped to form a core through which the water is pumped up, and an annulus into which the water is returned. The length of the central pipe at the bottom is coarsely perforated to form a diffuser. Water is drawn into diffuser and up this central riser pipe. The well pump is usually located at some depth below the water table in-line with central riser pipe. The standing column well combines the supply and diffusion wells into one, and is not dependent upon the presence or flow of ground water, although fractures in the bedrock that allow flow across the well can enhance performance, and reduce the length of the water column.

In practice, standing column wells are a trade-off between the open well systems and the below discussed closed loop earth coupling. The standing column well has the an advantage during the design phase in that the performance can be predicted without an extensive hydro-geological study. The savings in design fees and the elimination of the time period required for the hydro-geological analysis are attractive.

Given that standing column wells are unambiguous in projected performance, the use of this type of geothermal heat exchanger in most of Manhattan, the Bronx and northern Queens, where near surface bedrock can be anticipated is recommended. The standing column well can be designed and expected to perform to specification without the need for a test well. A heating or cooling capacity of 480 to 600 MBH (thousands of Btu/hr, equivalent to 40-50 tons of cooling) can be reliably expected from a 1,500 foot deep standing column well.

Should multiple wells be required, the spacing should be at least 50-75 feet. Closer spacing will affect the performance of the well field as the earth has a limited capacity to accept and reject heat. The diminished performance can be projected with available design software (typically GLPRO, see below).

Geothermal re-injection well water is considered a Class V water use and is regarded by the EPA as a 'beneficial' use. Permitting or notice may be required dependent upon average daily water flow rates. SCW wells shall be installed and serviced by qualified and experienced geothermal well contractors.


Long Island Power Authority (LIPA, formerly Long Island Lighting Company) has installed open loop geothermal heat pumps in four of its buildings over the past six years, see table 2a - 1 - LIPA facilities.

Facility__Design Load Completed

Brentwood 180 tons 1994 retrofit of 1958 geo system

Riverhead 80 tons 1997

Garden City 80 tons 1998

Hewett 100 tons 2000

Table 2a - 1 Long Island Power Authority Two Well (Open) Geothermal Heat Pump Installations

Of particular note is the Brentwood facility3, designed with an R-12 ground source heat pump installation in 1958. The facility has two wells, one a supply and one a diffusion well, both operational since 1958. The facility is a 6,500 square feet, two story building, providing office accommodations for 300 operating staff, and hosts a large cafeteria. Some offices, lockers and workshops are located in the basement, which also houses eighteen geothermal heat pump modules. The water to water geo-thermal heat pump modules replaced two 350 kW and one 900 kW gas fired boiler. The original wells and pumps were retained, but with a new variable frequency drive (VFD) which provides additional operational cost savings. A conceptual schematic of the system is shown in figure 2a - 7.

Note the modules are not centralized as in most other commercial applications. Each of the existing air handlers was left unmodified and was provided with matching capacity of heat pump modules. A comprehensive Honeywell system is employed to control each of the modules, air handler pumps and other related controls.

The Brentwood facility has been available to qualified engineering and design professionals for review and is well documented.

Based upon the success of the Brentwood operation, subsequent installations were made at the Riverhead operations facility, the Garden City Office and the Hewett Office. The Hewett Office has tied the geothermal heat pumps into a hybrid cooling tower system.


1 High density polyethylene pipe is specified as 3408 resin with a cell classification of 345434C or 345534C; pipe should be marked along its length with these specifications. Suppliers in the New York area are Driscopipe, Charter Pipe, Vanguard Plastics and others.

2 Typical GSV 048 heat pump for HEATING at 35°F, 36.9 mbtuh (3.56 COP) vs. at 20°F, 31.4 mbtuh (3.12 COP). For COOLING at 70°F, 50.9 mbtuh (17.9 EER) vs. at 90°F 47.1 mbtuh (13.7 EER)

3 Long Island Lighting Co., Brentwood Facility, ClimateMaster 97-BB101-9410-0, July 30, 1994

Permitting Requirements of Geothermal Heat Exchangers in NYC

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  • hiewan
    How many feet per ton for geothermal vertical loop "New york"?
    1 year ago

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